This invention relates generally to ignition systems for vehicles and is more particularly concerned with improvements in ignition systems for motorcycles.
Most gasoline engines incorporate an ignition system including a source of electricity (battery or magneto), a device to increase the electrical voltage, a breaker to determine the proper timing of electrical impulses, distributor means to send high voltage current to each cylinder of the engine in proper order, a spark plug in each cylinder, and wiring and switches to tie the system together.
In most motorcycle gasoline engines, the primary components of the ignition system comprise a battery, spark coil and distributor. The coil or spark coil generally has a primary coil made up of several hundreds of turns of wire, a soft iron core and this is connected in series to the battery. The secondary coil is generally produced from an extremely fine wire and comprises as many as 10,000 turns around the primary coil; the secondary coil is connected to the distributor. When the flow of low voltage current in the primary coil is momentarily interrupted, a high voltage current, as high as 30,000 volts, can be produced and flows through the secondary coil to the spark plugs.
To break the low voltage current in the primary coil, a pair of breaker points are opened and closed quickly, generally by a rapidly revolving cam, and these breaker points may be opened for as little as five thousandths of a second for each spark being generated. The opening of the points is timed to take place at a moment substantially before the piston reaches the top of the compression stroke of the cylinder, i.e., when the fuel is compressed. A condenser is generally attached to the pair of breaker points to draw off current which might otherwise cause sparking between the rapidly opening points. This condenser helps to provide a clean electrical break which is important in generating the proper spark characteristics. The high-voltage current is necessary to "push" across the fraction-of-an-inch gap of the spark plugs in the engine cylinders and must be hot enough to ingnite the compressed fuel. In engines with large cylinders, such as the Harley Davidson.TM. motorcycles, for example, it is conventional to use one spark plug in each cylinder. Generally a two lobed cam is used to fire the spark plugs.
Although various types of ignition systems are used in the operation of motor vehicles with small internal combustion engines, the most common ignition system utilizes a circuit breaker block assembly which includes a pair of points which are caused to open and close in synchronization with engine rotation through an integrated rotating shaft upon which a cam is mounted. Typically, these points are electrically connected to open and close the primary winding of an ignition coil. In typical circuit breaker systems, such as that found in the Harley-Davidson.TM. motorcycle, a single ignition coil fires both spark plugs simultaniously during each complete engine cycle; the first spark occurring immediately before the power stroke and igniting the compressed air/fuel mixture, while the second spark occurs as a consequence of the plugs being connected in series. This system, or variants thereof, have been incorporated in multi-cylinder motorcycle engines particularly since the multi-cylinder engines have provided the greater power and smoother operation than could be obtained through the use of single cylinder engines.
A problem which has manifested itself with the utilization of circuit breaker systems in combination with multi-cylinder engines has been the development of a spark during the intake stroke of the engine. Where the intake gases are ignited in the cylinders, this results in development of fire in the carburetor on the engine, a rough-running and noisy engine, and a reduction of power or efficiency.
This problem has been overcome in large internal combustion engines, through the utilization of a distributor, and attempts have been made to overcome the problem of ignition during an intake stroke of the engine by converting the motorcycle engine ignition system to a distributor-type as is explained in detail in the patent to Wyatt, Sr., et al., U.S. Pat. No. 4,315,487, issued Feb. 16, 1982.
Cylinders of relatively large size are provided with two spark plugs; and the switching mechanism includes dual breaker point assemblies, operated through the use of a lobed breaker cam; illustrative of this type of switching mechanism is the patent to McAllister, U.S. Pat. No. 3,221,116, issued Nov. 30, 1965.